Curable silicone compositions, especially the addition-curable silicone compositions, are widely used as dental impression materials. Generally, the addition-curable silicone compositions have the advantages of fast curing speed and low shrinkage. Furthermore, the cured silicone compositions have excellent physical properties, such as high mechanical strength and good dimensional stability. A considerable disadvantage of silicone compositions of this type, however, is their high hydrophobicity, which makes it difficult for them to take precise impressions when used on wet surfaces, such as the tissue, tooth or dental prosthesis in the oral environment in which blood, saliva, or other fluids usually exist.
The preparation of dental silicone impression materials by incorporating hydrocarbon, fluorocarbon or silicone-based surfactants, including ionic- and nonionic-type surfactants is known for imparting hydrophilic properties to these inherently hydrophobic substances and for improving the surface wettability. However, the addition of one or more surfactants to the compositions of the silicone polymers to impart hydrophilicity has drawbacks in that the surfactant molecules have a tendency to demix from the impression materials or migrate to the surface thereof, or the molecules are extracted from the impression material when it is contacted with aqueous media. Thus, the hydrophilicity of the impression materials cannot be retained when subjected to the procedures of rinsing with water, disinfection and sterilization required in dental clinic practice. Furthermore, when the surfactant is added in a large amount to obtain satisfactory water wettability of the cured silicone composition, the curing reaction of the composition is hindered, and the cured silicone composition has poor physical properties such as low tensile strength, elongation and tear strength. Particularly, the loss of surfactant due to contact with aqueous media results in undesirable dimensional change of the cured silicon composition.
Attempts have been made to render silicone dental impression materials more hydrophilic by adding hydrophilic additives into the curable silicone compositions. Hittmair et al. in U.S. Pat. No. 4,035,453 discloses the methods of making dental impression materials using curable silicone compositions. Bryan et al. in U.S. Pat. No. 4,657,959 and Aasen et al. in U.S. Pat. Nos. 4,691,039 and 4,752,633 disclose adding an ethoxylated nonionic surfactant containing siloxane or perfluoroalkyl solubilizing groups to achieve a three-minute water contact angle below about 65.degree.. Fujiki et al. in U.S. Pat. No. 5,064,891 discloses a curable silicone composition comprising a nonionic surface active agent having a hydrophobic silicone portion and at least one hydrophilic polyol portion in its molecule. Kamohara et al. in U.S. Pat. No. 5,637,628 discloses a dental impression-taking silicone composition comprising a polyvinyl ether having a degree of polymerization of 1,000 to 50,000. Hare in U.S. Pat. Nos. 5,661,222 and 5,863,965 and Fiedler in U.S. Pat. No. 5,830,951 disclose two-component polymerizable polyvinylsiloxane compositions comprising mono- and quadri-functional resins (QM) and nonylphenoxypoly (ethyleneoxy) ethanol surfactant. Zech et al. in U.S. Pat. No. 5,750,589 discloses a dental impression material containing polyether carbosilane as a hydrophilation agent. Jada in U.S. Pat. No. 5,852,068 discloses a dental impression composition comprising a dimethicone-based polysiloxane polyester polymer having terminal fluorinated alkoxy substituents. Paradiso in WO 93/17654 discloses a dental impression material comprising mono and quadri-functional QM resins. Gribi in EP 0 231 420 B1 describes the use of siloxane components having polyether moieties in the molecule.
The prior art hydrophilic additives in the silicone impression compositions suffer from certain drawbacks including unstable hydrophilicity when in contact with aqueous media and reduction in the physical properties such as tensile strength, elongation and tear strength. Accordingly, it would be desirable to provide an improved curable silicone impression material having a stable hydrophilic nature, excellent mechanical properties, and maximum long-term dimensional stability.